Why the RB25DET?

[JimmyJames1]

After researching RB's for a little while I can't seem to find a major reason why one would want to do an RB25 instead of an RB20. Hp difference is only 30 in stock form, and the price of an RB25 clip plus mounts and driveshaft is around $4500 before shipping ($3400 for the clip+$1100 for McKinney mounts & driveshaft). Price of an RB20 clip is $1900 at DragDriftAutox.com and other places. I know if you are going to have a completely built engine, the RB25 will yield more horsepower in the end, hoiw many of us are planning on having a completely built engine? Seems to me for the $2600 price difference you could easily surpass an RB25 performance wise. The only negative I have noticed about RB20's is the amount of problems people seem to be having with them, judging from posts on this board. However, this could just be the ratio of RB20's to RB25's. Anyway, this thread isn't to bash the RB25, I'm just curious why one would do that instead of RB20.

[Project240]

The RB25 is much easier to get power out of with simple mods, due mostly to the larger displacement. You can get 300HP out of boost increases and exhaust and minor stuff, while the RB20 requires a different turbo, minor fuel upgrades and some other little things to hit that level. Basically the RB20 is more like an SR20 in terms of general power potential (i.e. you can boost to about 250HP safely on the stock turbo, you start to reach the limits of the stock internals at about 400HP, etc), whereas the RB25 has much higher potentials (~350HP on the stock turbo?? I'm not sure, and 500, 550HP potential on stock internals).

It all depends on what your goals are. I went RB20 because of price, and because of the fact that I'm looking for more of a well-balanced car rather than a dyno queen. ~300WHP, good brakes, stiff suspension, lightweight chassis, and a clean body....should be enough to hang with all but the fastest sports cars.

[jt1583]

ya but is it going to cost you the 2600 dollars difference to make the rb20 as good as the rb25? i think not

[Nameless EJ6]

It's dead obvious.. it's all displacement and internal strength. Project240 summed it up quite nicely. You get much better power increases with simple mods with half a liter more of displacement...

[BoostFab]

gas milage, rb20 vs rb25?

[krayton]

as an RB25 owner, honestly, Id say the RB20 is the way to go. Just the fact that supply and demand rocketed the clips price. They used to be 1800 for a RB25 clip. at least you can still get the rb20s for a decent price.

but the bigger engine will always be able to make easier hp.

I think the RB20 has proven itself to be a good engine though. But its all just money. So if you have the money then go big.....which would be the rb26

oh and my orginal gas milage with the RB25 was 22mpg. after switching to the rb20 turbo it fell to 18mpg

[BoostFab]

oh and my orginal gas milage with the RB25 was 22mpg. after switching to the rb20 turbo it fell to 18mpg

that could be due untuned??!?!

[JimmyJames1]

Ok, so say my hp goals are going to be 350whp. Should I forget about RB25 and do RB20. Also, are RB20's less reliable than RB25's. Even if mileage is comparable, all RB20's are going to be older seeing as they were only made for R32's. And is it really $2600 to make the RB20 as good as a stock RB25?

[JimmyJames1]

Ok, so say my hp goals are going to be 350whp. Should I forget about RB25 and do RB20. Also, are RB20's less reliable than RB25's. Even if mileage is comparable, all RB20's are going to be older seeing as they were only made for R32's. And is it really $2600 to make the RB20 as good as a stock RB25?

[cyris3d]

id rather go sr20 then rb20.... way less wieght.. same tuneablity

[jbanach77]

also from what i have been told the rb20 transmission is not a strong trans past 400+whp, that is if you plan on going that far in the hp range

[Nameless EJ6]

Wow, if I was in your position I think I'd just turbo the KA motor. It's got the displacement you need, and you can probably hit 300whp with it stock. Then I'd invest in building it if I wanted more...

[Project240]

With a new turbo, fuel and tuning you can see 350WHP on an RB20 without too much trouble.

SR20s are less weight, but RB20s are inline 6s *purrrrrrr*

[cyris3d]

6 cylinder or not.. there is no real benifit for going rb20 over sr20.. sr20+TONS.. and i mean TONS more AM support..way Less wightSame Out put potential..(as long as displacement says the same)cheaper in the long runEz install(bolt in, super easy wiring)many Sr20s with t3/t4 and fuel running 400+ Hp stock bottem endfew with t3/t4s fuel and head werk 540+ stock bottem end

my opionin rb20s are junk and not worth the hassel, only kool factor is that you can say you have a skyline motor.. just my opinoin..

[Project240]

Yeah, I bought for the fact that it was an inline 6 (everyone had an SR, I wanted something at least a little different), and the low initial cost. The cost of everything thus far to get it driving, though, suggests that the RB20 swap isn't as cheap as it seems

[SeVa-S13]

Well my install is still going to come in far less than an SR, I'm going to sound a million times better than a 4 banger, I didn't have to buy a special mount kit and driveshaft, I don't have to worry about breaking a rocker arm if I redline, 2 extra cylinders are nice, and not every other 240 in the area has an RB20 (To be more precise, Project240 and I are the only ones so far).

And yes, I thoroughly enjoy realizing that I have a god damn Skyline engine in my little rice rocket.

[Project240]

Yes, I forgot about the sound. A built SR20 may have much more power than my car and the install may have been simpler, but it will never make the same beautiful sound I have emanating from my tailpipe

I only want about 300HP anyway :P

[NISMO_RB25]

My reasons to choose the 25:

1) newer engine (1997 in my case)

2) more displacement, and more potential

3) If I was going to add the weight of the 6, I wanted more power to start with (and torque)

4) I was going to use a mount kit anyway, to avoid the clearance issues (sway bar, hood, shifter, steering)

With all that said the SR20 is a swap I would highly consider, especially now that it hit 100 today and I don't have AC in the RB, but would have kept it with the SR.Thankfully I have another car with AC.

2K more and you could always go RB26

Good luck with your choice!!

[BoostFab]

i think it come down to budget, if you have enough money on hand--definately go with the most potential motor within your mean.

[Yellow4g63]

6 cylinder or not.. there is no real benifit for going rb20 over sr20.. sr20+TONS.. and i mean TONS more AM support..way Less wightSame Out put potential..(as long as displacement says the same)cheaper in the long runEz install(bolt in, super easy wiring)many Sr20s with t3/t4 and fuel running 400+ Hp stock bottem endfew with t3/t4s fuel and head werk 540+ stock bottem end

my opionin rb20s are junk and not worth the hassel, only kool factor is that you can say you have a skyline motor.. just my opinoin..

But if you say that about the 20 then same holds true for the 25. SR20 sawp is just plain cheaper if you look at it like that.

[cyris3d]

hence why im going 26.... ive sat down and thought about it many times.. i think if i wasnt gonna go rb26.. i woulda been better off goin sr20.. with the money ive put into the 25 i coulda had a really nice, fully built sr20 setup

[Nurv]

The RB20 is great and you are looking at it from a price point of view. The rb25 is a great buy and I know about the price difference. While I still lived in Dallas, Tx there was a guy trying to pass of a 25 as a single turbo 26 and sell it for $5500. I went and looked at it since it was in the cluip. I told him what I thought and he said I was right...Anyways, back to what im saying. RB20 is older and is upgradeable, yes but not worth it. Even with 2 more cylinders its not gonna be much better than a SR20. Hell if I went SR on my friend's 240 i was performing some driveline work i wouldve gotta some Toda ProCams and the 2.2 stroker kit. Torque is the pushing force and the more you have, the better off you are. If you are budget minded and only wanting $300-250whp this can easily be achieved by simple boltons to the SR as long as you dont care for the torque difference. Just my .02

[goofynick6]

SR's are more expensive than rb20's in most cases (if you want a decent SR motorset), and hey, call me old fashioned, but no matter how fast a car is, if it sounds like the SR's, it pretty much sounds like sh*t (nothing personal anyone that has one).

My tally so far:

RB20DET/trans/ecu/harness - $950XTD Clutch and fidanza flywheel $630Hybrid FMIC kit with everything $620Cleaned 550CC RX7 injectors $200Greddy E-manage (dont' have yet) ~$350T3/T04E 50 trim (don't have yet) ~$400Custom downpipe and mounts (done by me) $75Custom intake manifold (done by me) ~$100Gasket kit for engine ~$140Z32 MAF - Basically got freeWalbro 255 $80Misc stuffs? ~$120

That's $3,665 and enough parts there to make 400whp with proper tuning. That includes all shipping and install, etc. With that much, you can basically get a decent RB25 clip and an exhaust. I've been able to space out my buying of things so as to make it seem like less of an expense (rather than a lump sum for the RB25) and my engine will have new gaskets and seals, big turbo and injectors, fmic and e-manage to tune it all up with.

I know installing and welding stuff myself saves money, but if you got the RB25, you'd still need the FMIC kit, custom mounts, driveshaft, MAF, turbo, etc. etc.

For those reasons, I got the RB20 and I only want 350whp. With it's lighter weight and potential that meets my needs, the RB20 is perfect. If I wanted 500whp, I'd go RB25, but I don't, so I'm set.

Nick

[NISMO_RB25]

if i got a rb20 for under a 1K, I probably would have gone that route as well!

[goofynick6]

Yeah, I got lucky and found a guy in the next state looking to get rid of it since he needed money.

Nick

[Yellow4g63]

SR's are more expensive than rb20's in most cases (if you want a decent SR motorset), and hey, call me old fashioned, but no matter how fast a car is, if it sounds like the SR's, it pretty much sounds like sh*t (nothing personal anyone that has one).

My tally so far:

RB20DET/trans/ecu/harness - $950XTD Clutch and fidanza flywheel $630Hybrid FMIC kit with everything $620Cleaned 550CC RX7 injectors $200Greddy E-manage (dont' have yet) ~$350T3/T04E 50 trim (don't have yet) ~$400Custom downpipe and mounts (done by me) $75Custom intake manifold (done by me) ~$100Gasket kit for engine ~$140Z32 MAF - Basically got freeWalbro 255 $80Misc stuffs? ~$120

That's $3,665 and enough parts there to make 400whp with proper tuning. That includes all shipping and install, etc. With that much, you can basically get a decent RB25 clip and an exhaust. I've been able to space out my buying of things so as to make it seem like less of an expense (rather than a lump sum for the RB25) and my engine will have new gaskets and seals, big turbo and injectors, fmic and e-manage to tune it all up with.

I know installing and welding stuff myself saves money, but if you got the RB25, you'd still need the FMIC kit, custom mounts, driveshaft, MAF, turbo, etc. etc.

For those reasons, I got the RB20 and I only want 350whp. With it's lighter weight and potential that meets my needs, the RB20 is perfect. If I wanted 500whp, I'd go RB25, but I don't, so I'm set.

Nick

That list of mods sounds like 350 shouldn't be a problem for you. My friends FWD SR20 hit 319 with mods close to what you have. I wish I knew how much Hp I was looking for I'm just throwing stuff at the motor and taking it one day at a time. Wish AEM would hurry up and make the EMS for the RB's and 300zx's. They have the SR20 ones ready to go That alone makes me wish the guy I was goin to get my Redtop from didn't lag on me Ahh well I'll see if I can become a internet hero